Creo Simulate > Reference Links > Boundary Faces
  
Boundary Faces
Creo Simulate highlights all boundary faces—faces that belong to only one solid. Although these are not actually errors, you can check each boundary face to make sure it does not represent a missing element.
If your model contains boundary faces that are not associated with a surface, Creo Simulate highlights just those faces separately. You can use this information to identify missing elements.
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